package config

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

// LoadDotEnv reads a dotenv file and sets each variable into the process
// environment unless it is already set (real environment wins). Supported
// syntax: KEY=VALUE, blank lines, full-line and unquoted inline comments,
// optional `export ` prefix, single- or double-quoted values.
func LoadDotEnv(path string) error {
	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return fmt.Errorf("open %s: %w", path, err)
	}
	defer f.Close()

	sc := bufio.NewScanner(f)
	for n := 1; sc.Scan(); n++ {
		line := strings.TrimSpace(sc.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		line = strings.TrimPrefix(line, "export ")
		key, val, ok := strings.Cut(line, "=")
		if !ok || strings.TrimSpace(key) == "" {
			return fmt.Errorf("%s:%d: not a KEY=VALUE line", path, n)
		}
		key = strings.TrimSpace(key)
		val = strings.TrimSpace(val)
		switch {
		case len(val) >= 2 && (val[0] == '"' || val[0] == '\'') && val[len(val)-1] == val[0]:
			val = val[1 : len(val)-1]
		default: // unquoted: strip trailing inline comment
			if i := strings.Index(val, " #"); i >= 0 {
				val = strings.TrimSpace(val[:i])
			}
		}
		if _, exists := os.LookupEnv(key); !exists {
			os.Setenv(key, val)
		}
	}
	return sc.Err()
}